Update jig docs for the move to voxpupuli/jig and refresh to current CLI

[miharp]

Summary

Update the jig docs for the tool's move to github.com/voxpupuli/jig and bring the prose in line with jig's current CLI. Implemented in #349.

What was done

Repo move

• Point all avitacco/jig links and the go install path at voxpupuli/jig.

Command and prose fixes

• Fix invalid commands in modules_publishing.markdown (jig module build, jig build build, jig module) to jig build.
• Document --skip-interview and its companion value flags on jig new module.
• Document the template-override precedence (the --template-dir flag, then the template_dir config key). The README's JIG_TEMPLATE_DIR env var doesn't reliably bind in the source, so it's left undocumented.

Discoverability and naming

• Point the PDK.markdown jig "alternative" entry at our own /ecosystem/latest/devkit/jig.html docs (keeping a repo link for source/releases) and capitalize the proper noun "Jig".
• Add a "see installation and usage" pointer from devkit/components.md to the scaffolding page.
• Add a cross-collection "Scaffolding modules with Jig" entry to the core OpenVox Modules nav (absolute path, per CONTRIBUTING).

jig validate / test unit / update

• migrating.md: map pdk update/validate/test unit to the jig commands, noting they wrap the underlying bundle exec calls.
• linting.md: note jig validate runs validate + lint (not lint_fix).
• unit_testing.md: add the run command (jig test unit, wrapping bundle exec rake spec).

Out of scope

The two overlapping publishing pages (_openvox_8x/modules_publishing.markdown and _ecosystem_8x/devkit/publishing.md) were left as-is. The jig docs live under the ecosystem collection, which tolerates more duplication than the core docs, so merging them wasn't worth it.